Two-way radio signaling system



Nov. 13, 1928. I 1,691,076

R. c. MATHl-:s

TWO-WAY RADIO SIGNALING SYSTEM Filed March l1, 1924 )f 2 S ee s-Sheet 1 /l. d

MMI/um? 1 R. C. MATHES4 Two-WAY RADIO SIGNALING SYSTEM Nov. 13, 1928. 1.691.076

Filed March 11, 1924 2 sheets-sheet 2 0 v //5 l f/J E 2 Y l A,

so ter.

Patented Nov. 13, 19,28.y

` UNITED STATES PATENTA OFFICE.;

ROBERT C. MATHES, OF` WYOMING, NEW JERSEY, ASSIGNOR T WESTERN ELECTRIC COMPANY, INCORPORATED, 0F NEW YORKpN. VY., A CORPORATION OF NEW YORK.

TWO-WAY RADIO sIeNALING SYSTEM.'

Application and iviarchii, i924. ssii-iai Nq. 698,353.1

This invention relates to two-Way radio signaling systems and particularly to a combined transmitting and receiving station of such a system. i

Tarrant for the term a combined transmitting and receiving station,` as distinguishedv from a. term suggesting separate functions andstructures for the component transmitting and receiving circuits, is found v lo in the close Y physical relationship between such circuits at ya station so designated. T here may be a common antenna for the two circuits; the circuit may be coincident at some other point; or the circuits may be entirely separate, but in close proximity to each other. The arrangements at suchstations are characterized by a' condition favorable to singing or at least to the production of side tone in the receiver from the local transn'iitu This condition is much more crit-ical in radiant energy systems than in similar systems utilizing lower frequency since in the former, on account of the high frequencies used, and distributed capacity as Well as other casual and unavoidable capacity is effective as an impedance element Whereas in the latter is negligible. Moreover in radio systems, as contrasted with wire systems, considerably larger amounts of energy are necessarily required in carrying out the transmitting function as compared with the amount of energy required to carry out the receiving function,

i therebyincreasing theliability of singingA or side tone production.

5 l.An object of the invention is to avoid singing or the. production of side tone in a receiving circuit of such av combined radio transmitting andreceiving station by energy from the localtransmitter.

Among the means that have heretofore been used in the attainment of the above object there are included commutation means, and specifically, relay operated switches to render the Vtransmitting and receiving circuits alternateey operative. In one specific formy of system embodying such a commutation means a portion of the outgoing energy, and specifically a portion of the sound or other forni of energy used for signaling transmission, is

used to energize the relays to actuate the switches in one phase of their movement,

mutation arrangement last described is that an appreciable time isk required, on account of the mechanical inertia of the moving parts of the relay, etc., tocompletetlie reorganilzation of the circuits preparatory totheir use for a new phase of operation. Since in a' system of this kindin which the circuits are normally biased to the receiving condition, the beginning of transmission from the; signaling source is coincident with the initiation of the switching operations, the completion of these operations does not occur lsoon enough to provide for the radiation of the iirst part of the signal, that is, the'signal transmission is clipped.

A further obfect of the invention accordingly is to control the Vresponsiveness of the receiving circuit and the operation of the, transmitting circuit at such a station directly by signaling energy and without clippingat the beginning oftransmission.

The above stated objects are realized, for example, in avoice controlled two-Way radio station in generaljresembling that above deV c ated switches have prepared. the transmitting circuit for transmission of the signals into space. v y

In an arrangement in which the 10W frequency portions of the transmitting and receiving circuits are connected, as is the vcase for example, where each is Vjoined to a common subscribers telephone circuit, the received v-low frequency current, to the extent that it could flow into ythe transmitting Acirrcuit at thejunct-ion point, would function in all respects like outgoing signaling current. Itfwould accordingly tend to cause,

through the transmission control circuit, ,a

reorganization of the circuits as a` whole in such a manner as to render them operative for receiving. This result Would tend to be brought about whether or not the delay cir- The delay circuit principle is used in a l receiving circuit ot this invention to insure that the operation, whereby the transmitting control circuit is rendered inoperative, will be completed before the received signal wave has progressed to the point ot connection ot the circuits. The use ot delay circuits in both the transmitting and receiving circuits ot radio systems,in combination with the various features described above, results in a close approach to the conditions ot operation in ordinary subscriber station circuits in wire telephony. l The particular means ot the invention are suiliciently effective 'tor their respective purposes as to permit the use ot the same carrier frequencies tor both systems ot transmission.

The delay circuits maybe loaded circuits of any type, ior erarnple, a. conventional wave ilter which consists of plurality oit sections the number and constants ot which are designed to give the requisite time lag.

The menace oit C:ide tone interference in the receivingcirc' rgry 'tromthe local rai emitter is reduce d by the above described operations whereby the transmittinov and rc ceiving circuits are alternately rendered operative. This result may be accomplished by affecting; the connections between the y an tennae (or the antenna it single antenna is used in common tor the two circuits) and the remaining` portions ot the transmitting and receivingT circuits. lt may `be alJ rernatively Yor additionally accomplisher, by a'ecting' the transmitting and receiving; circuits elsewhere than at the antennre. llor example, the transmitting circuit which normally inoperative inay be rendered operati Ye by increasing the grid polarizing; potent ot the grid ot a three element repeating` tubein series in the transmitting circuit to a value sui'licient to malte the space circuit cr ductive.

This invention includes a particu er n'ieans for changing the grid polarizing' potential as to prevent the generation et transients in the circuits, that would oth e be set up it the customary relay actiV ad switches were used to produce vail it the grid potential, because or" the rapid te at which th va 1iation would taire place. Such transie are detrimental to the best operation oi the system hence the feature of the invention whereby they are prevented is important. This particular' means involves the use of a space discharge tube repeater having' its tubes c nnccted in the so-called push-pull or bal anced relation and the common portion ot its grrid-lilament circuits arranfvcd to eiij'ect the desired crid potential variation. i

The invention will be better understood by roter-ence to the tollowing sr-ecilication and accompanying drawings in wl Ach:

Fig-g. l relnesonts in diagrammatic ,term the uits et a complete two-way radio station e invention; in'. 2 represents a circuit which may be solisti 1fl 'oi that portion ot lhg. l between lines le-X and if- Yr lli El represents a circuit which may be itcd tor that portion oit the circuit of Y or ot n in". l varied in accordance with at die right et points il, B, C, l), E the correspondence of letters in Figs. l innicating the manner et substituindicates la term et delay circuit which may be substituted vfor the blocks so Llied in the systems et Figs. l and 2. i the particular systems illustrated by l and 2, a common antenna AN is used ie transmf. tiny; and receivingl circuits, n 4s ot the trfnismitting` circuit being t the lett et the antenna and that ot eivingf circuit at the right. The an- 's connected 'to one circuitor the other according to the position et the switch l which is normally held in the receive position i s which is capable et being` actuated by relav to take the transmit position. This 1' itch is illustrated as in the receive posi- -1'on, to which it is normally biased by means viwn. Theother switches 3, 5, 7 and 9 are snnilarly biased to their normally inoperative positions illustrated. Y

l" cggarding' tor the moment the control circuits including' the relays and their relati" prises, in substantially the order given, the low frequency line L, the amplifier A, the

circuiti DC, the modulator M, the osi or 0, the balanced ampliiier BA and the antenna All, by which combination the sigoin low trequency line L are amplified d are then used to modulate the current illator O, after which the signal l wave is amplified and radiated. ions and elements `lor perform- .rc cach conventional in Vcarrier sys* not require turther description y circuit may be simply a loaded in line designed to give a uniform i to the various frequency coinmalfzincg up the signalingcurrent. illustrated in Fig. o, which s purpose, consists of series switches, tno transmitting` circuit comi llO , in a paper eiititled;Physical theory ot the 40 y the second numbered paragraph on page 10.Y

inductances and shunt capacities. It may be a. low pass filter ot the type disclosed atlg in Fig. 1l ci' United States patent to Campbell, No. 1,227,114 `granted May 22, 1917, although a delay circuit is not required tov have the cli'i `acteristies ot' a filter. Delay circuits per se and the spec-ille torni of 5 are the invent-ions ol" H. D. Arnold and are disclosed in his United States Patent 1,565,302, December 15, 1925.

Delay circuits of the types disclosed are 'forms of loaded lines haring series induetances and shunt capacities. The manner in which a loaded line acts to slow down transmission is discussed iii U. S. patent toY Pupin 652,231, J une 19, 1900, to which reference may be made forpan explanation of their` operation.

A physical explanation of a phenomenon inite' velocity is, almost by definition, a progressive change of phase throughout the length of the circuit. VAccordingly, a circuit whose operation is characterized by such change of phase is, to that extent, a delay circuit. Artificial networks, whose sections are similar to those ofcominercial filters, operate in this manner within their transmission ranges. A physical, as distinguished iii-oni amathematieal,explanation is given electric wave-filter7 by C: A; Campbell which appears in the Bell System Technical Journal for November,Y 1922. See particulary llhat there must be this progressive change et' phase troni section to section of a filtersniiulating network for each frequency within the transmission range Vmay be eX- plained very siinply,`aud incre brieflyfthan in Campbells paper above cited. This eX planatioii is in accordance with a method which has heretolore'been used only with reference to .mechanical wave filters, rbut it is equally applicable to electrical filter-sini4 ulating networks. Y

iissuine the most general case of such network having the characteristics of a band filter. of which the netuferk of F 5 which ulatcs a low pass filter is a vlimiting case. .c also that there is no resistance in the Consider first the frequency at indiictance and shunt capacityo't' each in resonance and the current is attenuated. The reactions lOll litt Cw cf' therefore not from the shunt capacities are not effective on er cut-oli`f Aft this frequency the se-` pacity) so that there isno longer resonance ot the two elements. This condition results in a phase shift in the .series section, as coinpared with the; condition at the lower cutofl' ti'equency, and therefore the series and shunt currents are no longer iii phase quadra.- ture, so that the shunt capacity lends a portion of its reaction to assist that of the series capacity to preserve the necessary equality of reactions, which equality' indicates a condition of non-atteiiuation.l A i llii s phase shift is repeated for each section. A different shift increasingwith the frequency, occurs iler each frequency with- .l

in the range. t certain critical frequency there is 160"A phase shift per section. This corresponds tog'the condition et inaxiinum Accordingly, currents having frequencies greater than this value must work against an' lexcess mass reaction and are therefore attenuated. This frequency thereiore corresponds to the upper cut-oli'.

Currents having' `rfrequencies below the lower cut-oit are similarly Iattenuated as could easily be demonstrated hy aconiplcmental inode of reasoning. Currents having` frequencies below the lower cut-of have Zero phase shift and their propagation velocities are therefore infinite; For currents having frequencies above the upper cutfofi' the phase shifts remain at 1800 so that the velocities.otpropagation are finite, but obviously on account or the attenuation char-V acteristic the network cannot be used as a delay circuit for suoli currents. The delay, of course, is greater for frequencies nearV 'the upper cut-ofi than for those near the lower cut-ofi. A lter-*simulating network can therefore be used as a delay mrcuit for rtreyquencies within its transmission range.

that

corfre- 7 i r section i a 500 cycle wave, 10() sections 'would be required to cause a delay cfa tenth of a second.

i/:ing the eilect of increasing mass reac- For eX- y if there was a phase shift of 180O fue The balanced amplifier is o the type disclosed in United States patent to Colpitts No. 1,128,2927 granted February 16, 1915, TVhen the switch 5 is closed, as during; the receiving phase et operation at the station, the negative potential ot battery ll is added to that or battery l2 to malte the amplilier inoperative for transmission. lWhen the switch is opened, by relay G, the amplifier is made operative. Y

The receiving' circuit comprises the antenna AN, the detector-amplifier Dit the delay circuit DS1 `and low frequency line la by means ot which received signal waves are amplilied and detected to reproduce a signmlV frequency current which is transmitted through the delay circuit to the .low trequency line. The delay circuit may be like or unlike that used in the transmission circuit.

The low frequency portions oit the transmittingg` and receiving; circuits are conmcted to the common line L through a three winding transformer T and network N by means ot' which the connection may be made substantially conjugate. i

ln the twoway system ot l the provision ot a single antenna connected alternately to the transmitting' and receivino circuits insures that these circuits are alternately operative., and hence that the condition ot the circuits as a whole is unfavorable to sine:- ingr. rlhe signal control means tor accomplishing' this and similar functions, will new be described.

Antenna AN is svitche'd to its transmit position by relay 2 which actuates switch l. Relay 2 is in the transmitting control circuit together with relays l and 6 which similarly actuate switches 8 and 5. Although these relays are shown connected in series they may equally well be connected in parallel. The use ot the additional relay actuated switches further insures against singing. Switch 3, for instance, is normally biased to t ie circuit closing' position. and is actuated to the circuit open position coincidently with the actuation or switch l, to produce a secondary break iu the re eivinfr circuit. lnstead ot producing;` a break this switch may be used in an obvious manner to short circuit the receivingr` circuit. Switch 5 isV normally biased to circuit closed position to maintain the balanced amplifier and oscillator' in the transmittino; circuit. in an inoperative condition and: is actuated to circui.A open position coincidentlv with the actuation ot switches l, and 8 to increase lthe grid potendals and acemdine'ly to malte the transmitting circuit operative.

Relays 2, a and (i are included in a circuit branched from the signal transmission' circuit and are energized by the operation ot the sie'- nal current after rectilication in the rect Ayingr device Alt which ordinarily. althouc'h not nece. sarily. would ampli-ty as well rectify. Additional amplification may be Vrelays to open the receiving circuit.

Ation by causing' a portion of the detected low obtained by separate stages et amplifiers it desired. rl'he delay circuitlQC insures that the various switching functions are comi pleted and accordin'g'ly, the circuit as whole prepared "for transmission, in time to permit the tiret part of the signal to be transmitted and radiated troni the antenna. lts use ac cordingly prevents clippingw ot the lnitted signal.

'lhe balanced amplilier having' the switch 7. in the common portion. ot the eritfiilament circuits has the important function preventing the settingrup ot transients that would otherwise result trom the sudden change ot 2grid potential. These transients so would tend to atl'ect the receiving circuit in much the 1e way as static hummes incident on the rece circuit. litho ich there is no conductive connection between the high 'frequency portions ot the trans uit if and 83 receiving; circuit. these tran ni'ght easily have sullicient intens' l dutively atleet the receiving' circuit. An important advantage in the et large power stations, i infr 'from switching' bv 90 shuttinggj oil the space current in the pow auipliliei the savingv in transmitted pov-Je tiet is altected during: the time when signal t ansmission is not taking' place.

ln the circuits et Fi l as so tar described the connection between the low frequency portions et the transmittingand recivinlej circuits results in a difficulty not present where such circuits are seiiarate.y that it. it provides a path for the detected low irequency current to enter the transmitting circuit. rlhe E and netbalanced transiormer work is not etl'ective under practical conditions to prevent the Atlow ot a quantity ot this energy suilicient to actuate vthe transmitting); The etlect would immediately when the switches haebeen actuated, whereupon the bia-singv means would restore th circuits to their initial condition. This cycle ol operation would be repeated at a periodici? determined by the natural period of mechanical movement of the switches. Y

rlhis eitect isfavoided in the present invenlll) frequency, after amplification and rectification in device AR, to actuate switch 7 through relay 8. -This operation renders inooerative the transmitting circuit and particularly the control circuit branched therefrom. The current which actuates switch .7 through relay 8 also actuates switch 9 through series relay l() to remove a short circuit 'from the low frequency portion ot' the receiving' circuit. This switch is normally biased to its closed ist position and comprises hne ot the several i ients which cooperate to prevent singing1 or intenter-ence during' transmission..

The delay circuit DQ `functions in a inanner similar to the delay circuit in the trans- 13u mitting circuit to -insure that the received signal is not clipped duringthe operation of switch 9. It also functions to prevent the operation of switches 1, and 5, by'v eceived energy before switch 7 ate. V v Y y Fig. 2 illustrates a circuit which maybe substituted for that included between lines X--XV and Yf-Y. The elements having similar functions are identified inthe same manner as in Fig. 1. The modified arrangement differs functionally vfrom that of Fig, l only in that the transmitting circuit isiiiade operative by effectively connecting the carrier oscillator to the modulator, instead of affecting the impedance of the amplifier. Specifically the step is accomplished by removing the short circuit from the oscillator O, which normally exists by reason of switch 5, by

`means of relay actuated switch 5. Amplifier A, may be used, if necessary, to amplify the modulated carrier current. Although this amplifier may be of the balancedtype as in F ig. 1, the reasons urging its use inthat circuit are not here present, kand a single tubel amplifier would be practically as effective.

Figs. 3 and 4 illustrate modifications of similarly labeled portions of the circuits of Fig. 1. In the arrangement 'of Fig. 3, although the antenna is not alternately connected to the transmitting and receiving circuits, it is nevertheless alternately put in energy transfer relation to ysaid respective circuits lby the switching means illustrated. That is, switch 1 is opened by relay 2 to remove a short circuit on the coil 13 in the antenna circuit which coil functions during transmission as the secondarysof the oscillation'transformer. The receiving-circuit is effectively uncoupled from the antenna by switch 3 and relay 4. An advantage possessed by the circuit of Fig. 3 over that of Fig. 1 is that the. two operations take relatively less time for their completion since'the antenna is made operative for transmission by theopening, instead ofthe-closing, of a switch. As al result the problem of designingl a delay circuit having the requisite time lagV is more simply and less expensively met.

The arrangementof Fig.. 4 is alternative to that of Fig. 3 and the corresponding portions of Fig. 1; The figure illustrates the applicationl of the principle of the. arrangementof Fig. 3`to the case of separate transmittingly and receiving antennae.

The receiving antenna AN1 maybe a loop as illustrated or any other conventional form of receiving antenna. The directional selective properties of a receivingloopmakes it possible to secure additional discrimination from locally transmitted energy by its use in this circuit. l

The means for making the antenna effective for transmission differs from that of Figz in that, instead of effectively coupling the yantenna to vthetransmitting circuit, the switch has had time to oper- 1 and relay 2 effectfachange in the resonant frequency of the antenna` from a .conditiony unfavorable to a condition favorable to transmission.v

i In the arrangement of Fig. 1 modified by 7o the,ysubstitutionVV o' thecircuits of Fig. 2, the switch 1- has additionaladvantages not resulting from the use ofthecircuits of Fig. 1 unchanged. These additional advantages result from the fact that in such a modified systeni the power amplifier isnot edectively removed'from the circuit as in Fig. 1. In powerful stations in which the ratio of transmitted tofreceived power is enormous, the inl cidental disturbances in tlie power amplifier Y 8oY would tend to set up transients in the outgoino antenna which would seriously alect incoming transmissionNThis is avoided by switch 1 which disconnects the power amplifier from the antenna during reception. vThe co 'responding 'means inFigs. 3 and 4 are similarly effective to prevent this particular type of'interference.

rlhe novel features believed to be inherent o, in ythis linvention are disclosed in the appended claims.' v

W' hat is claimed is: 1. A signaling circuit comprising a source of modulating waves, means-utilizing the waves from said source for producing a sig-V nal modulated wave, and means for transmitting the elements of saidmodulated wave at equa-i `predetermined intervals of time after the production of corresponding elements of the ymodulating wave, said last mentioned lmeans,comprising a .delay circuit between said .source and said first mentioned means. p

2. A two-way radio signaling station coml prising normally operative receiving cir- Wi cuit, a normally inoperative,transmitting circuit, means operative only during. the pro-- duct-ion of a signal modulated wave for rendering said circuits respectively inoperative and operative, and means for preventing the UU impression of said wave on the transmitting circuit during theoperation of said means. ,y 8. A two-wayradic signaling station comprising a normally inoperative transmitting circuit, means for' generating a signal modu- 115 lated carrier wave, .means operative only during the production of said wave forzmalking said circuit operative, and means for prei vei'iting the impression of said wave on said circuit during'the operation of said second'WU y .mentioned means. y

4. A. two-way yradio signaling station com-y prising a normally inoperative transmitting circuit, means for producing a .signal modulated' wave, means'operative onlyduring the 125 aroduction of said wave for renderingsaid` circuit operative, and automatic means for preventing 'the clipping of the signal trans-- mission during the operation ofV said second mentioned means.:

Cil'

5. A tivo-Way radio signaling station comprising a transmission circuit, means normally making said circuit inoperative, means tor generating a signal modulzdedl Wave, means `operative only during said generation and dependent thereon for maintaining said circuit in zin-operative condition, and means for preventing the clipping ot the signal transmission during the operation of said third-mentioned means.

6. In combination, a source oic signal Waves, means for modulating high frequency carrier Waves in accordance with said signal Waves, radio transmission circuit, means i'or renderingat least one portion oi' said circuit at times inoperative for transmission, means for rendering said portion at other times operative 'tor transmission, and means whereby each element of said modulated Wave is incident on said portion nearest to said source predetermined definite time atterthe gen-eration olf said signal Waves.

'i'. In combination, means ii'or generating a signal modulated current, a circuit for translating said current into ether waves, means for rendering at least one portion of said circuit normally inoperative tor transmission,

mea-ns operative only during said generation and dependent thereon lor making said circi t op tive, and automatic means whereby said generated' Wave isA incident on said portion ncarestto the generating means only atteiall oi said portions have been made operative for transmission.

8. ln combination, means for generating a signal modulated current, circuit for translating said .current into ether Waves, means normally rendering at least one portion otsaid circuit inoperative for transmission, signal-actuated means for making and maintaining said portions operative during said generation, and a delayT circuit in said circuit :tor preventing the impression ot' said waves on said portions untilthey have been made operative igor transmission.

In combination a source ot signal current, a source ot carrier frequency cu 1rent,

means for modulating said carrier current inaccordance with said signal current, a circuit for `translating said modulated current into ether Waves, means normally rendering at least aportion of said circuit inoperative for transmission, means actuated by signal current. tor making and maintaining said portions ot the circuit operative, and a delay circuit tor preventing modulation oi the carrier current by the signal current before said portions have been made operative.v

l0. ln combination, a source oi signal current, source ot carrier frequency current, means for modulatingrsaid carrier Vcurrent in accordance With said signalcurrent, a circuit for translating sai o .modulated current into ether Waves, means `normally rendering at least one portion of said circuit inoperative tor transmission, a lrelay-containing circuit connected to said signal current source for rendering said portions operative duringsignal c rrent generation, and adelay circuit between said signal current source and said modulator for preventing modulation until said portions have been made operative'.

ll. ln combination a source oi sigggnalingV current, a source of carrier current, means i'or modulating said carrier current in accordance with said signaling current, radiating means, a transmission circuit connecting .said n'iodula'ting and radiating means, means normally rendering said circuit inoperative for transmission, means normally rendering d radiating .ieans inoperative :tor radiating, means responsive to the signal current. for making said circuit-,and radiating means operative, and a. delay circuit for preventing clipping of the Vsignal While said last mentioned means is being operated.

l2. ln combination, a `signal current source, a carrier current source, a radiating mez'ins, means tor generating and transmitting to said radiating means a signal modulated carrier current Wave and including a three-element electric discharge device having anode, cathode, :and an impedance controlling element, means for normally .affecting the potential of the impedance controlling element to make the electric `dischargfje device inoperative, means 'l'or'at times adocti-ng the potential of said impedance controlling element in a different sense to malte said electric discharge device operative, and means whereby a change of potentialY of said in'ipedance controlling element is effected-independent ot the production of transients in the output circuit of said electric discharge means.

13. The circuit speciiied in claim 12 in which the electric discharge means comprises balancecl three-element electric discharge devices each having a cathode, an anode,l and an impedance controlling grid, and in which the means affecting the impedancecontrolling grid operates on the com non cathodegrid circuit. i g

111-. ln combination a signal current source, a-carrier current source, means for modulating said carrierfcurrent in accordance with the signal, radiating means, a transmission circuit between the modulator and radiating means and including a thermionic discharge amplifier, comprising a cathode, an anode, and an impedance controlling grid, means normally impressing a bloclting potential on the grid of said amplifier, means for at times removing the blocking potential from said grid, and means tor preventing-the production oli' transients in the output circuit of V l amplifier when the potential ot its grid is changed.

15. The circuit specified in claim 14- in which the amplifier comprises-two ythermionie soY vtial on the grid of electric discharge ,devices each having a cathode, an anode, and an impedance cons trol ing grid, the grid-cathode patlis for tlie tufo devices having portions ink common and A other portions individual to each device and iii which the means for inserting andrenioving the blocking potential operates on the common portions of the grid-cathode paths.

16. In combination a signal current source,

a carrier current source, means for modulating said carrier currentA in accordance with the signal current, radiating means, a transmission circuit between Vtlie modulator and' radiating means and including an electric discharge ampliiier including a cathode, an anode and an impedance controlling grid, means normally impressing a blocking poten` said amplifier, means responsive to tlie signal current for removing,` the blocking potential. from the grid ofy said amplifier, said amplifier blocking andremoving means including a ii'ieansv for prevent' the production of transients in the output ci i'- cuit 0f the amplifier by a change of grid potential.

17. The circuit specified in claim 16 but ini cluding additionally Va delay circuit between tion, the means for impressing and remov-v ing the blocking potential being operated on the common portions of tlie grid-cathode paths of thetwo devices.

19. A two-way radio signaling station comprising in combination a signal current source, :i carrier current source, modulating means for said currents, radiating means, transmission circuit connecting said modul ating means and radiating means, a low frequency circuit connecting said signal current source and modulating means, a receiving circuit including a demodulator, a second loiv frequency circuit connected to said deinodu lator` individual circuit closing means nor# mally biased to respectively render lsaid transmitting circuit inoperative, to render said second low frequency circuit inoperative for transmission, to. render said receiving cir cuit operative for reception, and to connect said radiating means in energy transfer relation to said receiving circuit, a signal re-,

sponsive means operating on certain ofsaid circuit closing means to render said transmission circuit operative for transmission, to

, render said receiving cii'cuit'inoperative for reception, and to connect said radiating means in eiiergy'transfer relation to saidv transmission circuit,- and means responsive to tlie deniodulated low frequency current foroperating on other of said circuit closing means to render said second low frequency Y circuit operative for transmission.

20. A two-way radio signaling system comprism iii combination a low frequency line, a

Acommon radiating and receiving means, a

transmitting and a. receiving` circuit connecting said line and radiating means, said 4trans-v mitting circuit coinprising'a low frequencyl portion, a carrier current source, a. modulat-A liigli and low frequency portions, separate circuit closing` means normally biased to render tl'ie amplifier and the low frequency portion of tlie receiving circuit inoperative for current transmissicnlto render tlie liigh/ freing inea/ns and a power amplifier, and saidreceiviiig circuit including a deiiiodulator'and Y quency portion ef the receiving circuit eperative for recept-ion, and to connect the common radiating` mean-s o 'the receiving circuit, a

transmission control circuit branched from the low frequent-y portion of the transmitting circuit and including relays in energy transfer relation to the circuit closing means associated with tlie amplifier, radiating means and liigli frequency portion of the receiving circuit wher-eli)T said circuit closing means Vare operated responsively to said signal currentsa receiver controlk circuit branched from the low frequency portion of vthe receivingcircuit and including relays in energy trans-Q fer relation to tlie circuit closing means associated with the low frequency portion of tlie'receiver circuit, av circuit closer in said transmission control circuit normally biased to circuit closing position, and a second relay in saic receiver control circuit, whereby the circuit closer associated with the low frequency portion of the receiving circuit and tlie circuit closer in the transmission control circuit are actuated responsively to low fre'- qiiency demodulated current.

21. The circuit of claim 20 including ad ditio-nally a delay circuit between the point of connection of the ,transmission control circuit to the low frequency portion of the'transinitting circuit and the modulator, for preventi ng the clipping ofthe transmitted signal during the eperationof the transmission con-l trol circuit, and a delay circuit vbetween tlie point connection of tliereceivingcontrol,

circuit to the receiver circuit and the circuit closer in tlie loiv frequency portion lof the receiving circuit, for actuating said last men-` tioned circuit closer and for making inoper'a-' tive the transmission control circuit before the demodulated current is impressed upon the. loiv frequency portion of the receiving circuit. Y Y

22. In a two-,way radio signaling system, a

transmission circnii'o coinprisingI s signal cnrreni; source, a carrier currentv soins-e, means for modulating said carrier current in accordence with said signal current d a power amplifier, a receiving circuit, a connnon an ienne, means norinally'based 'to ccnneclA4 said antenna in energy transfer relation lo said receivingl circuit, ineens normally biased lo disconnect said carrier current source roin energy transfer relation to said inodnlainfg means, and ineens for actuating said normall5' biased means to respectively change "che connection oi' said anienns Ylfroni lie receiving circuit to the transmitting; circuitand to connectsaid carrier current source in ene transfer relation to said modulating means,

23. ln a two-Way radio signaling; system7 a transmission circuit comprising a. signal source7 a carrier curren source, ineens 'for modulating said carrier ciirreniU in accodance With said signal curreni and a power aniilifier, s receiving circuit, a common antenne, means normally biased to conductively connect said antenna exclusively to seid receiving' circuit, means normally hissed to disconnect ln e radio system for t-ransniiiting and receiving' signalk modulated Waves, a normal- Vy niol eratlve cransrni'tnig circuitwv s non ially operative receiving' circuit?v said circ-niis being coupled to low frequency line, an anX- il' iry circuit ari Lng'ed to control said trans niiiicing and receiving circuits, said auxiliary circuit being effective io open said receiving' circuit prior 'go the transmiseionoil energy from said transmitting circuit and to stop i'i nsniis ion oi? energy from said ransmitin fxcircnii; prior io the 'transmitting of signal Wares to said low frequency line.

ln Witness whereof, l hereun'o subscribe my naine this lili day of March, A. D. 1924:.

ROBERT i Ariens. 

